Hmm for mining you basically don't need an app you need the hardware, you need to have a mining machine based on various components you can visit the Mining section the Bitcoin for the component guide. As you are saying app probably means that you want to start cloud mining and there are various cloud mining platforms legit and scams as well so be aware. Even though last few weeks ago I heard Binance is also providing cloud mining not sure I'll have a look again and then catch you up.

My recommendation is that cloud mining is rewarding but you have to buy the hash rate there as well and it's less rewarding as with hash rate they provide you the consent reward of the pool, self Mining is more recommended because there is a risk but highly rewarding if by luck you compete the current Hash rate and mine a single block haha it will be the reward beyond the reach comparing to could mining.